Mask for euv lithography and method of manufacturing the same

ABSTRACT

A mask for extreme ultraviolet (EUV) lithography includes a multilayer (ML) stack including alternating metal and semiconductor layers disposed over a first surface of a mask substrate, a capping layer disposed over the ML stack, and an absorber layer disposed over the capping layer. An image pattern is formed in the absorber layer. A border layer surrounding the image pattern is disposed over the absorber layer.

TECHNICAL FIELD

The present disclosure relates generally to a photo mask (reticle) forextreme ultra violet (EUV) lithography, and a method for manufacturingthe same.

BACKGROUND

EUV lithography is the most promising technology for semiconductordevice manufacturing of the 10 nm node and beyond. In EUV lithography,an EUV photo mask is one of the key elements. For an EUV photo mask,multiple mask parameters should be optimized to achieve precise and highresolution pattern forming in EUV lithography. Such parameters include,but are not limited to, an absorber height, optimum optical proximityeffect corrections (OPC) needed for shadowing correction, an increase ofreflectivity in image fields and optimum image borders.

EUV photo masks have a black border area, over which mask blades of anEUV lithography tool are placed. The black border is a pattern free darkarea around the die on the photomask serving as transition area betweenparts of the mask that are shielded from the exposure light by thereticle masking (REMA) blades and the die. When printing a die at densespacing on an EUV scanner, the EUV light reflection from the imageborder overlaps edges of neighboring dies. This reflected light alsocontains various wavelengths that are not required, known as out-of-band(OOB) light. The OOB light adversely affects the accuracy of patterns tobe formed on a substrate, in particular sections around the periphery ofthe pattern on the substrates. Additionally, leakage of EUV radiationoccurs during exposure of adjacent dies because of residual absorberreflectivity and REMA blade instability, resulting in over exposurearound die edges. To reduce this effect, a black border area is placedbetween adjacent dies. The black border area can solve CD non-uniformitycaused by neighboring die exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 schematically shows a black border formed around an image fieldin a EUV mask.

FIG. 2 schematically shows the effect of a black border region inreducing undesired exposure of adjacent dies.

FIG. 3 schematically illustrates a cross-section of an EUV mask blankused for making an EUV mask in accordance with an embodiment of thepresent disclosure.

FIG. 4 shows a flow chart for a process of fabricating an EUV mask inaccordance with an embodiment of the present disclosure.

FIG. 5 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 6 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 7 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 8 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 9 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 10 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 11 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 12 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 13 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 14 schematically illustrates a cross-section of one of the variousstages during a process of fabricating an EUV mask in accordance with anembodiment of the present disclosure.

FIG. 15 schematically illustrates a cross-section of an EUV mask inaccordance with an embodiment of the present disclosure.

FIG. 16 schematically shows a plan view of an EUV mask in accordancewith an embodiment of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus/device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly. In addition, theterm “made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

In EUV photolithography, the EUV light rays emitted from a plasma arereflected off a collector mirror, directed toward a patterned EUV mask,and reflected off the EUV mask onto the target substrate. An EUVreflective mask includes a substrate, an EUV reflective multilayered(ML) structure, and an EUV absorbing layer (‘absorber’). The EUVabsorbing layer is patterned by etching portions of the absorbing layerto expose the underlying ML structure in those portions to form adesired pattern. EUV radiation is reflected from the exposed MLstructure on to a target substrate coated with a EUV resist. Theportions of EUV absorbing layers left unetched absorb the EUV radiationso as not to reflect EUV radiation on to the target substrate, therebyforming the desired pattern on the target substrate.

In various embodiments, a layer of photosensitive material (sensitive toeither EUV) is provided on the target substrate and exposed to an EUVbeam reflected from the EUV mask. In some embodiments, the targetsubstrate is an unpatterned wafer, and in other embodiments, the targetsubstrate has one or more patterned layers with patterns previouslyprinted using lithography, deposition and/or etching processes. Inembodiments where the EUV mask includes, for example, test structuresused for calibration of a wafer pattern, an unpatterned substrate isused to avoid complexities resulting from uneven surface of a patternedsubstrate. In some embodiments, the unpatterned substrate includes asilicon wafer with a layer of silicon dioxide or silicon nitride on top.The thickness of the silicon dioxide or silicon nitride is notparticularly limited. In such embodiments, the photosensitive layer,e.g., of a photoresist material, is disposed on the silicon dioxide orsilicon nitride layer, e.g., by spin coating, exposed to EUV radiationbeam reflected from the EUV mask, and developed to form a patternedphotoresist layer on the wafer. The pattern is then printed on the waferby etching the silicon oxide or silicon nitride layer using thepatterned photoresist layer as an etch mask. The photoresist layer isthen removed in some embodiments. However, in some embodiments, forexample, where measuring the characteristics of the photoresist itselfis of interest the photoresist layer is not removed. In suchembodiments, processing steps can be reduced by leaving the silicondioxide or silicon nitride layer unetched.

The thickness of the EUV absorbing layer, the thickness of each of thelayers in the ML structure, surface roughness of the above layers, andthe homogeneity of the material properties throughout the layersdetermine the quality of EUV radiation irradiating the target substrate.In industrial practice, off-axis illumination or other factors can causea shadow effect on the target substrate and variations in the thicknessof the EUV absorbing layer can affect the proper functioning of thecombination of the EUV absorbing layer and the ML structure.

FIG. 1 schematically shows a black border formed around an image fieldin a EUV mask. The ‘black border’ 150 is formed at the edge of thedesired patterns (i.e., image field 125) of the EUV reflective mask 100to avoid over-exposure of the edge of the patterns in an adjacent die.The ‘black border’ is a non-reflective area formed to prevent exposureof adjacent dies because of residual absorber reflectivity, off-axisreflection shadow effects, OOB light, etc.

FIG. 2 schematically shows how the black border reduces undesiredexposure of adjacent dies. Radiation R incident on the black border 150(despite the presence of ReMa blades 220) is absorbed by the blackborder 150, preventing exposure of the edge region of the adjacent die240 adjacent to the current die 250.

In some implementations, the black border 150 is formed by etching apredetermined area around the circuit pattern to form a non-reflectivetrench of sufficient depth for destructive interference of any reflectedEUV radiation from that region. However, the additional etching stepalso requires additional photolithography steps which increases theprocessing time and consequently increases the probability of damage tothe circuit pattern on the mask. Moreover, the additional etching stepmay result in particulate residue diffusing on to the circuit patterncausing undesired defects. Such implementations of the black border are,therefore, susceptible to longer processing times and lower yield.

To alleviate some of these disadvantages, in some implementations, apredetermined region around the circuit pattern is laser annealed fromback-side of the mask (i.e., substrate side rather than the patternside) to intentionally change the ML structure and thereby, change thereflectivity of the ML structure at the desired wavelength. However,because the change in the reflectivity of the ML structure in such aprocess comes about due to physical and chemical changes induced byheat, it is difficult to precisely control the area in which suchchanges occur, thereby potentially damaging the image region. Alternateforms and methods of forming black border for EUV mask are, therefore,desired.

The present disclosure generally relates to EUV masks, and in particularto a non-reflective “black border” for EUV masks, and a method formaking EUV masks with the non-reflective black border. The EUV mask andmethods of making the EUV masks provide for formation of a black borderregion without substantial additional lithographic processing or heatingsteps, thereby avoiding the problems of potentially damaging the imageregion.

FIG. 3 schematically illustrates a cross-section of an EUV mask blankused for making an EUV mask in accordance with an embodiment of thepresent disclosure. In an embodiment, an EUV mask blank 300 includes amultilayered EUV reflective (ML) stack 320 disposed over a first majorsurface of a mask substrate 310. A capping layer 325 is disposed on theML stack 320, and an EUV absorbing layer or absorber 330 is disposedover the capping layer 325.

In some embodiments, as depicted in FIG. 3, an antireflection layer 335is disposed over the absorber layer 330, and a conductive backsidecoating layer 315 is dispose on the second major surface of the masksubstrate 310 opposite the first major surface on which the ML stack 320is disposed. The conductive backside coating layer 315 is used to fixthe mask for photolithographic operation by electrostatic chucking insome embodiments. In an embodiment, the conductive layer 315 is formedof a ceramic compound including CrN, CrO, TaB, TaBN, TaBO, TaO, TaN, Taor any suitable material for electrostatic chucking of the mask.

The mask substrate 310 is made of a low thermal expansion glass materialincluding titanium oxide doped silicon dioxide, or any other suitablelow thermal expansion materials such as quartz, silicon, siliconcarbide, and/or other low thermal expansion substances known in the artthat can minimize the image distortion due to mask heating in the EUVphotolithographic environment, in some embodiments. In some embodiments,the mask substrate 310 has a low defect level, such as a high puritysingle crystal substrate, and a low level of surface roughness, asmeasured using an atomic force microscope.

The ML stack 320 includes alternating Mo layers and Si layers depositedover the mask substrate 310. The ML stack 320 provides Fresnel resonantreflections across the interfaces between the Mo layer and Si layer ofdifferent refractive indices by use of an appropriate thickness for eachlayer inside the ML structure. High quality reflections rely onconstructive interference by phase-matching and intensity adding-up oflight rays reflected from different layers. The thickness of the layersdepends on the wavelength of the incident light and the angle ofincidence to the EUV mask blank 300. For a specific angle of incidence,the thickness of each of the layers of the ML stack 320 is chosen toachieve maximal constructive interference for light reflected atdifferent interfaces of the ML stack 320. Thus, even thickness and lowsurface roughness of each of the layers in the ML stack 320 are requiredfor high quality Fresnel resonant reflections. A thickness of each ofthe layers in the ML stack 320 is about 3 nm to about 7 nm in someembodiments.

In some embodiments of the present disclosure, the ML stack 320 includesalternating molybdenum layers and beryllium layers. In some embodiments,the number of layers in the ML stack 320 is in a range from about 20 toabout 100 although any number of layers is allowed as long as sufficientreflectivity is maintained for imaging the target substrate. In someembodiments, the reflectivity is higher than about 70% for wavelengthsof interest e.g., 13.5 nm. In some embodiments, the ML stack 320includes about 30 to about 60 alternating layers of Mo and Si (or Be).In other embodiments of the present disclosure, the ML stack 320includes about 40 to about 50 alternating layers each of Mo and Si (orBe).

Methods of forming the layers of the ML stack 320 include, but are notlimited to, physical vapor deposition (PVD) processes such asevaporation, RF or DC sputtering; chemical vapor deposition (CVD)processes, such as atmospheric-pressure, low-pressure, plasma-enhanced,and high-density plasma CVD; atomic layer deposition (ALD); ion beamdeposition; and liquid-phase non-vacuum methods such as a sol-gel methodand metal-organic decomposition; and/or any other suitable method knownin the art.

The capping layer 325 formed over the ML stack 320 prevents oxidation ofthe ML stack 320 in some embodiments. In some embodiments, the cappinglayer 325 is formed of a material such as, for example, silicon andruthenium. In some embodiments, the capping layer 325 has a thickness ina range from about 2 nm to about 7 nm. Methods of forming the cappinglayer 325 include, without limitation, ion beam deposition, (IBD),physical vapor deposition (PVD) processes such as evaporation, RF or DCsputtering; chemical vapor deposition (CVD) processes, such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods, such as a sol-gel method and ametal-organic decomposition; and/or any other suitable method known inthe art.

The EUV absorbing layer or absorber 330 formed over the capping layer325 absorbs radiation having a wavelength in a range of EUV wavelengths,e.g., at 13.5 nm. The EUV absorbing layer 330 is formed of a singlelayer or multiple layers in some embodiments of the present disclosure.In some embodiments, the EUV absorbing layer 330 is formed of a materialincluding a tantalum compound. In some embodiments, the EUV absorbinglayer 330 is formed of TaN or TaBN. In some embodiments, the materialused to make the EUV absorbing layer 330 also includes molybdenum,palladium, zirconium, nickel, nickel oxide, nickel silicide, titanium,titanium nitride, chromium, chromium oxide, aluminum oxide,aluminum-copper alloy, or other suitable materials.

Methods of forming the EUV absorbing layer or absorber 330 include, butare not limited to, physical vapor deposition (PVD) processes, such asevaporation, RF or DC sputtering; chemical vapor deposition (CVD)processes, such as atmospheric-pressure, low-pressure, plasma-enhanced,and high-density plasma CVD; atomic layer deposition (ALD); ion beamdeposition; and liquid-phase non-vacuum methods, such as a sol-gelmethod and a metal-organic decomposition, and/or any other suitablemethod known in the art.

The anti-reflection layer 335 disposed over the EUV absorbing layer 330is formed of a material including SiO₂, SiN, TaBO, TaO, CrO, ITO (indiumtin oxide), or any suitable material, in some embodiments. Theantireflection layer 335 reduces residual reflection from the absorberlayer 330. In some embodiments, the antireflection layer 335 is formedof an EUV absorber material different from that of the absorber layer330. In other embodiments, the antireflection layer 335 is formed tochange a phase of any EUV radiation reflected from the absorber layer330 so as to reduce the intensity of the reflected EUV radiation viadestructive interference.

Methods of forming the anti-reflection layer 335 include, for example,physical vapor deposition (PVD) processes, such as evaporation, RF or DCsputtering; chemical vapor deposition (CVD) processes such asatmospheric-pressure, low-pressure, plasma-enhanced, and high-densityplasma CVD; atomic layer deposition (ALD); ion beam deposition; andliquid-phase non-vacuum methods, such as a sol-gel method and ametal-organic decomposition; and/or any other suitable method known inthe art.

An aspect of the present disclosure provides a method of fabricating anEUV mask having a black border region surrounding an image region. FIG.4 shows a flow chart for a method of fabricating an EUV mask inaccordance with an embodiment of the present disclosure. FIGS. 5-14schematically illustrate cross-sections of various stages during aprocess of fabricating an EUV mask in accordance with an embodiment ofthe present disclosure. In an embodiment, the method of fabricating anEUV mask includes, at S410, forming a hardmask layer 350 and a firstresist layer 355 on a mask blank 300. Specifically, as shown in FIG. 5,the hardmask layer 350 is formed on the antireflection layer 335, and afirst resist layer 355 is formed on the hardmask layer 350.

In various embodiments, materials suitable for forming the hardmasklayer 350 include, but are not limited to, silicon dioxide, siliconnitride, spin-on carbon, spin-on oxide, CrO, CrN, CrON, TaO, TaN, Ru,RuN, RuB, TaB, TaBN, TaBO and their oxynitride, etc. The material forthe hardmask 350 is not limited so long as it is different from (and hasetch selectivity over) that of the absorber layer 330. The hardmasklayer 350, in various embodiments, has a thickness in a range from about1 nm to about 100 nm. Methods of forming the hard mask layer 350include, but are not limited to, physical vapor deposition (PVD)processes, such as evaporation, RF or DC sputtering; chemical vapordeposition (CVD) processes, such as atmospheric-pressure, low-pressure,plasma-enhanced, and high-density plasma CVD; atomic layer deposition(ALD); ion beam deposition; and liquid-phase non-vacuum methods, such asa sol-gel method and a metal-organic decomposition, and/or any othersuitable method known in the art.

As shown in FIG. 5, the first resist layer 355 is formed over thehardmask layer 350. Examples of suitable resist materials for the firstresist layer 355 include, without limitation, e-beam resists such as,for example, PMMA, or other commercially available positive tone ornegative tone e-beam resists; or photoresists such as, for example, SU8or other commercially available positive tone or negative tonephotoresists. The first resist layer 355 is coated onto the hardmasklayer 350 by a spin coating technique followed by baking, in someembodiments.

At S420, the first resist layer 355 is exposed to actinic beam radiationand a developer to form an image pattern 650 in the first resist layer355, as can be seen in FIG. 6. In some embodiments, the actinicradiation includes an electron beam, while in other embodiments, theactinic radiation includes deep ultraviolet (DUV). In embodiments wherethe actinic radiation includes an electron beam, the first resist layer355 is formed of an e-beam resist such as PMMA and the image pattern 650is formed, for example, by a direct write process where a tightlyfocused electron beam is scanned across the surface of the first resistlayer 355 such that only the area corresponding to the image pattern isexposed to the electron beam. The e-beam resist is then developed toform the image pattern 650 in the first resist layer. On the other hand,in embodiments where the actinic radiation is DUV, a series oflithography steps (i.e., exposure through a mask followed bydevelopment) are performed to obtain the image pattern 650 in the firstresist layer because the wavelength of DUV radiation is typically a lotlonger than the CD of an EUV mask. The series of lithography steps, insome embodiments, include performing exposure under a liquid (i.e.,immersion lithography). In some embodiments, the series of lithographysteps are performed to obtain a pattern resolution that is higher thanthe pattern resolution obtained by a single lithography step. Forexample, in some embodiments, a single pattern is divided into two ormore interleaving parts, each having a CD longer than that of the singlepattern. The two or more parts of the single pattern are processedindividually while “covering” the other parts, and all the parts ofcombined in the end to provide a CD that is smaller than that of each ofthe individual parts. For example, a 25 nm half-pitch pattern can begenerated by interleaving two 50 nm half-pitch patterns, three 75 nmhalf-pitch patterns or four 100 nm half-pitch patterns.

The image pattern 650 formed in the first resist layer 355 is extended,as shown in FIG. 7, to the hardmask 350 by removing the portions ofhardmask 350 exposed through the image pattern 350 (see FIG. 6). In someembodiments, the exposed portions of hardmask 350 are removed byperforming dry and/or wet etching of the hardmask 350 using a suitableetchant. In other embodiments, the exposed portions of hardmask 350 areremoved using, for example, ion milling, or other suitable techniques.As shown in FIG. 8, once the image pattern 650 is formed in the hardmask350, the first resist layer 355 is removed in some embodiments.

The image pattern 650 is then further extended, as shown in FIG. 9, intothe antireflection layer 335 and the absorber layer 330 so as to formthe image pattern 650 on the mask blank 300. The extension of the imagepattern 650 into the antireflection layer 335 and the absorber layer 330is performed by removing portions of the antireflection layer 335 andthe absorber layer 330 that are exposed through the image pattern 650formed in the hardmask 350. The removal of the exposed portions of theantireflection layer 335 and the absorber layer 330 is performed by dryand/or wet etching using a suitable etchant. Once the image pattern 650is formed in the antireflection layer 335 and the absorber layer 330,the hardmask 350 is removed, as can be seen in FIG. 10.

At S430, a second resist layer 360 is formed as shown in FIG. 11. Thesecond resist layer 360, in some embodiments, is formed by disposing thematerial of the second resist layer (referred to herein as the secondresist material for brevity) over the absorber layer 330, having theimage pattern 650 formed therein, and spinning the substrate at asuitable rotational speed to form a suitable thickness of the secondresist layer 360. The rotational speed, in some embodiments, isdetermined based on the viscosity of the material of the second resistlayer 360 and the desired thickness of the second resist layer 360. Invarious embodiments, the second resist layer 360 is provided at athickness in a range from about 50 nm to about 1000 nm. In embodimentshaving the antireflection layer 335 the second resist layer is disposedover the antireflection layer 335.

In some embodiments, the second resist material includes a polymer and ametal oxide, a metal nitride or a metal oxynitride. In particular, insome embodiments, the second resist material includes a polymer andnanoparticles of a metal nitride or a metal oxynitride. Thenanoparticles have an average particle size in a range from about 1 nmto about 50 nm in various embodiments. Examples of suitable polymersinclude, but are not limited to, polyvinylalcohol (PVA),polyvinylpyrrolidone (PVP), poly(ethylene glycol) (PEG), polyamide (PA),polyacrylamide, poly(acrylic acid), poly(methacrylic acid), etc.Examples of suitable metal oxides include, without limitation, oxides ofAl, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Mo, Ru, Pd, Ag,Te, Ta, W, Jr, Pt, La, Ce, etc. Examples of the metal nitride includetransition metal nitrides such as TiN, ZrN, WN, TaN, etc., or p-blocknitrides such as AlN, BN, Si₃N₄, etc. Examples of oxynitrides include(stoichiometric or non-stoichiometric) transition metal oxynitrides suchas titanium oxynitride, etc., or p-block (stoichiometric ornon-stoichiometric) oxynitrides such as aluminum oxynitride. Othernitrides and oxynitrides of the same metals as those suitable for metaloxide are also contemplated. The weight ratio of polymer to metal oxide,metal nitride or metal oxynitride is in a range from about 9:1 to about50:1 in various embodiments.

In various embodiments, the second resist layer 360 is formed of amaterial having a dose dependent resist tone. For example, in anembodiment, the material of the second resist layer 360 (referred toherein simply as “second resist material” for convenience), is an e-beamresist having a positive resist tone for a first exposure dose (e.g., alow exposure dose) and a negative resist tone for a second exposure dose(e.g., a high exposure dose). A low exposure dose, as referred toherein, is a dose at which the developed resist has a positive tone, anda high exposure dose, as referred to herein, is a dose at which thedeveloped resist has a negative tone. In some embodiments, a highexposure dose is at least one order of magnitude higher than a lowexposure dose.

In some embodiments, the second resist material with a negative tone(i.e., following an exposure to actinic radiation at a second exposuredose) has a reflectance of less than about 3% for EUV wavelengths (i.e.,wavelengths in a range from about 5 nm to about 20 nm). In someembodiments, the second resist material with a negative tone has areflectance of less than about 1% for wavelengths in a range from about12 nm to about 14 nm. For example, in some embodiments, positive toneresist property is observed when the exposure dose is in a range fromabout 1 mC/cm² to about 50 mC/cm². In some embodiments, a negative toneresist property is observed for an exposure dose greater than about 50mC/cm².

In some embodiments, the second resist material with negative tone(i.e., following an exposure at the second exposure dose) has aroot-mean squared (rms) surface roughness in a range from about 0.1 nmto about 2 nm. Without wishing to be bound by theory, exposure of thesecond resist material at the second exposure dose causes agglomerationof the nanoparticles in the second resist material to form islands orbumps on the surface of the second resist layer 360, creating a roughsurface. Such surface roughness may further reduce undesired reflectionfrom the border region by scattering the EUV radiation incident on thesecond resist layer.

In some embodiments, the second resist material is formed using asol-gel process. In other embodiments, the second resist material isformed by dispersing nanoparticles of a suitable metal oxide, metalnitride or metal oxynitride in a suitable polymer.

At S440, a first exposure is performed on the second resist layer 360 ata first dose at which the second resist material has a positive tone.The first exposure is performed using the same pattern as the imagepattern in some embodiments. Following the first exposure, the positivetone second resist layer 360′, as shown in FIG. 12, covers theantireflection layer 335 and the capping layer 325 exposed through theimage pattern 650 formed in the absorber layer 330.

At S450, a second exposure is performed on the positive tone secondresist layer 360′ at a second dose at which the second resist materialhas a negative tone. As shown in FIG. 13, the second exposure isperformed using a pattern corresponding to a border pattern 560surrounding the image pattern 650. The border pattern 560, in someembodiments, is provided such that a negative tone second resist layer360″ covers the antireflection layer 335 in a portion 560 surroundingthe image pattern 650 at location that would reduce undesired exposureof image patterns adjacent the image pattern 650 on the exposure waferto be exposed using the EUV mask. In other words, the border pattern 560corresponds to a “black border” region.

At S460, the second resist layer 360′, 360″ is developed to remove thepositive tone resist layer 360′. A bake step is performed beforedeveloping the second resist layer, in some embodiments, to pre-cure theresist material and reduce the amount of solvent in the resist material.Following the development operation, the second resist layer 360″ isleft behind covering portions of the antireflection layer 335corresponding to the border pattern 560, as can be seen in FIG. 14,because of its negative tone. If necessary, a hard bake step isperformed following the development of the second resist layer tofurther harden the negative tone second resist layer 360″ in someembodiments.

In some embodiments, the second resist material is a negative toneresist that is exposed to a suitable dose only in the regioncorresponding to the border pattern 560. In other embodiments, thesecond resist material is a positive tone resist that is exposed to avery high exposure dose (e.g., greater than 100 mC/cm²) in the regioncorresponding to the border pattern 560 resulting in sintering of thepositive tone resist and causing it to behave like a negative toneresist in the region corresponding to the border pattern 560. In otherwords, it is possible to achieve negative tone behavior in a positivetone resist.

Another aspect of the present disclosure includes an EUV mask having ablack border region around an image pattern. FIG. 15 schematically showsa cross-section of an EUV mask in accordance with embodiments of thepresent disclosure. In an embodiment, the EUV mask 400 includes asubstrate 310 and a multilayered EUV reflective (ML) stack 320 disposedover a first major surface of the mask substrate 310. A capping layer325 is disposed over the ML stack 320, and an EUV absorbing layer orabsorber layer 330 disposed over the capping layer 325. Portions of theabsorber layer 330 corresponding to an image pattern 650 are removed. Aresist layer 460 is disposed on portions of the absorber layer 330surrounding the image pattern to form a border region 560.

In some embodiments, the EUV mask 400 is formed using the EUV mask blank300 shown in FIG. 3. The description of the substrate 310, the ML stack320, the capping layer 325, the absorber layer 330, and theantireflection layer 335 is provided elsewhere herein. The EUV maskblank 300 is processed to form the EUV mask 400 which includes an imageregion 650 where portions of the absorber layer 330 are removed. Theremoved portions correspond to areas of a circuit pattern which are tobe exposed to the EUV radiation. Thus, EUV radiation incident of mask400 is reflected from the image region 650 on to the wafer to be exposedusing the EUV mask 400, thereby exposing the photoresist coated on thewafer to the EUV radiation and form the circuit pattern in thephotoresist.

The mask 400 further includes a border region 560 where a resist layer460 is disposed on top of the absorber layer 330. The border region 560is selected to provide a black border for the image pattern so as toreduce undesired exposure of dies adjacent to the die being exposedduring a given exposure using the mask 400. In various embodiments, theresist layer 460 has a thickness in a range from about 20 nm to about1000 nm.

In an embodiment, the material of the resist layer 460 (referred toherein simply as “resist material” for convenience), is an e-beam resisthaving a positive resist tone for a first exposure dose (e.g., a lowexposure dose) and a negative resist tone for a second exposure dose(e.g., a high exposure dose). In some embodiments, the resist materialwith a negative tone (i.e., following an exposure to actinic radiationat a second exposure dose) has a reflectance of less than about 3% forEUV wavelengths (i.e., wavelengths in a range from about 5 nm to about20 nm). In many embodiments, the second resist material with negativetone has a reflectance of less than about 1% for wavelengths in a rangefrom about 12 nm to about 14 nm.

In some embodiments, the resist material includes a polymer and a metaloxide, a metal nitride or a metal oxynitride. In particular, in someembodiments, the resist material includes a polymer and nanoparticles ofa metal oxide, metal nitride or a metal oxynitride. The nanoparticleshave an average particle size in a range from about 1 nm to about 50 nmin various embodiments. Examples of suitable polymers, metal nitrides,metal oxides and metal oxynitrides are discussed elsewhere herein.

In some embodiments, the resist layer 460 is formed of a negative e-beamresist. In other words, only the portion of resist layer 460 exposed toan electron beam is left behind after being developed. In otherembodiments, the resist layer 460 is formed of a positive e-beam resistwhich is hard-cured (e.g., exposed to a very high exposure dose) in theborder region 560 and unexposed in the image region 650 such that onlythe portion of resist layer 460 exposed to an electron beam is leftbehind after being developed. The term “hard-cured,” as referred toherein, means that a positive e-beam resist exposed at dose at which theresist polymerizes to “harden” as if it were a negative resist.Typically, positive e-beam resists are hard-cured at exposure doses thatare one or more orders of magnitude higher than a “normal” exposure dosefor a positive resist.

Another aspect of the present disclosure provides an EUV mask having ablack border region around an image pattern. FIG. 16 schematically showsa plan view of an EUV mask in accordance with an embodiment of thepresent disclosure. In an embodiment, the EUV mask 400 includes apattern region 650 and a border region 560 surrounding the patternregion 650. In some embodiments, the border region 560 is formed of aresist material having a dose dependent resist tone, and a reflectanceof less than 3% at wavelengths in a range from 5 nm to 20 nm followingan exposure to a dose of actinic radiation at which the resist materialhas a negative tone. In various embodiments, the border region 560 has athickness in a range from about 20 nm to about 1000 nm.

In an embodiment, the resist material is an e-beam resist including apolymer and a metal oxide, a metal nitride or a metal oxynitride. Insome embodiments, the resist material includes a polymer andnanoparticles of a metal nitride or a metal oxynitride. Thenanoparticles have an average particle size in a range from about 1 nmto about 50 nm in various embodiments.

In some embodiments, the resist material has a positive tone at lowexposure dose and a negative tone at a high exposure dose.

In some embodiments, the border region 560 is formed of a negative toneresist material having a reflectance of less than 3% at wavelengths in arange from 5 nm to 20 nm after being cured. In yet other embodiments,the border region 560 is formed of a positive tone resist material thatis hard-cured by exposing at a very high exposure dose. The positivetone resist in such embodiments, has a reflectance of less than 3% atwavelengths in a range from 20 nm to 1000 nm after being hard-cured.

The various aspects described in the present disclosure provide for anEUV mask with black border region around an EUV mask so as to reduceundesired exposure of adjacent dies on substrate to be exposed to EUVradiation. The black border region, in various embodiments, is formedusing a resist material that is exposed at an appropriate dose such thatthe resist material in the border region is hardened and the resistmaterial in the image region is dissolved away during development.Methods of making EUV masks according to the present disclosure avoidetching steps which can potential degrade other layers of the EUV maskand/or create particulate contaminants. Embodiments of the presentdisclosure also avoid the ill-controlled physical and/or chemicalchanges of the reflective ML stack in the border region by laserannealing the ML stack in the border region from a backside of the EUVmask. The black border formed using the embodiments described herein canbe formed at a high-throughput without the addition of costly or timeconsuming process steps.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

According to one aspect of the present disclosure, a mask for extremeultraviolet (EUV) lithography including a multilayer (ML) stackcomprising alternating metal and semiconductor layers disposed over afirst surface of a mask substrate, a capping layer disposed over the MLstack, and an absorber layer having an image pattern formed thereindisposed over the capping layer. A border layer surrounding the imagepattern is disposed over the absorber layer. In some embodiments, theborder layer includes a resist material. In some embodiments, the resistmaterial includes a polymer and a metal oxide, a metal nitride or metaloxynitride. In some embodiments, the border layer has a rms surfaceroughness in a range from about 0.1 nm to about 2 nm. In someembodiments, the resist material includes metal nitride or metaloxynitride particles having particle size in a range from about 1 nm toabout 50 nm. In some embodiments, the border layer has a thickness in arange from about 20 nm to about 1000 nm. In some embodiments, the resistmaterial includes a negative photoresist or a negative electron-beamresist. In some embodiments, the resist material includes a hard-curedpositive tone resist.

According to another aspect of the present disclosure, a method ofmaking an EUV lithography mask includes forming a hardmask layer over amask blank and a first resist layer over the hardmask layer. The maskblank includes a multilayer (ML) stack disposed on a substrate, acapping layer disposed on the ML stack and an absorber layer disposed onthe capping layer. An image pattern is formed on the mask blank bypatternwise exposing the first resist layer to acitinic radiation andremoving a portion of the first resist layer. The image pattern istransferred to the hardmask layer and the absorber layer. A patternedresist layer is formed over the absorber layer and surrounding the imagepattern. The patterned resist layer exposes the image pattern. In someembodiments, the forming the patterned resist layer includes disposing asecond layer of a material of the patterned resist layer over theabsorber layer having the image pattern. The second layer is patternwiseexposed to expose an area of the second layer surrounding the imagepattern to the actinic radiation at an exposure dose at which thematerial has a negative tone. The second layer is then developed to formthe patterned resist layer on the area surrounding the image pattern. Insome embodiments, the material of the patterned resist layer includes apolymer and a metal oxide, a metal nitride or metal oxynitride. In someembodiments, the material of the patterned resist layer includes metalnitride or metal oxynitride particles having particle size in a rangefrom about 1 nm to about 50 nm. In some embodiments, the patternedresist layer has a thickness in a range from about 5 nm to about 500 nm.In some embodiments, the material of the patterned resist layer,following an exposure at an exposure dose at which the material has anegative tone, has a reflectance of less than 3% for wavelengths in arange from about 5 nm to about 20 nm. In some embodiments, the materialof the patterned resist layer has a positive tone at a first exposuredose and a negative tone at a second exposure dose higher than the firstexposure dose. In some embodiments, transferring the image pattern tothe hardmask layer and the absorber layer includes etching the hardmasklayer and the absorber layer.

According to yet another aspect of the present disclosure, a mask forEUV lithography includes a pattern region and a border regionsurrounding the pattern region. The border region has a thicknessgreater than that of the pattern region and includes a resist material.In some embodiments, the resist material has a thickness in a range fromabout 20 nm to about 1000 nm. In some embodiments, the resist materialincludes a polymer and a metal oxide, a metal nitride or metaloxynitride. In some embodiments, the resist material includes metalnitride or metal oxynitride particles having particle size in a rangefrom about 1 nm to 50 about nm. In some embodiments, the resist materialincludes a negative photoresist or a negative electron-beam resist.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A mask for extreme ultraviolet (EUV) lithography,the mask comprising: a multilayer (ML) stack comprising alternatingmetal and semiconductor layers disposed over a first surface of a masksubstrate; a capping layer disposed over the ML stack; an absorber layerhaving an image pattern formed therein disposed over the capping layer;and a border layer surrounding the image pattern disposed over theabsorber layer.
 2. The mask of claim 1, wherein the border layercomprises a resist material comprising a polymer and a metal oxide, ametal nitride or metal oxynitride.
 3. The mask of claim 1, wherein theborder layer has a root mean squared (rms) surface roughness in a rangefrom about 0.1 nm to about 2 nm.
 4. The mask of claim 1, wherein themetal oxide, metal nitride or metal oxynitride particles have an averageparticle size in a range from about 1 nm to about 50 nm.
 5. The mask ofclaim 1, wherein the border layer has a thickness in a range from about20 nm to about 1000 nm.
 6. The mask of claim 1, the resist materialcomprises a negative photoresist or a negative electron-beam resist. 7.The mask of claim 1, wherein the resist material comprises a hard-curedpositive tone resist.
 8. A method of making an extreme ultraviolet (EUV)lithography mask, the method comprising: forming a hardmask layer over amask blank and a first resist layer over the hardmask layer, the maskblank comprising a multilayer (ML) stack disposed on a substrate, acapping layer disposed on the ML stack and an absorber layer disposed onthe capping layer; forming an image pattern on the mask blank bypatternwise exposing the first resist layer to actinic radiation,removing a portion of the first resist layer, and transferring the imagepattern to the hardmask layer and the absorber layer; and forming apatterned resist layer over the absorber layer and surrounding the imagepattern, wherein the patterned resist layer exposes the image pattern.9. The method of claim 8, wherein forming the patterned resist layercomprises disposing a second layer of a material of the patterned resistlayer over the absorber layer having the image pattern; performing apatternwise exposure to expose an area of the second layer surroundingthe image pattern to the actinic radiation at an exposure dose at whichthe material has a negative tone; and developing the second layer toform the patterned resist layer on the area surrounding the imagepattern.
 10. The method of claim 8, wherein a material of the patternedresist layer comprises a polymer and a metal oxide, a metal nitride ormetal oxynitride.
 11. The method of claim 10, wherein the material ofthe patterned resist layer comprises metal nitride or metal oxynitrideparticles having particle size in a range from about 1 nm to about 50nm.
 12. The method of claim 8, wherein the patterned resist layer has athickness in a range from about 5 nm to about 500 nm.
 13. The method ofclaim 8, wherein a material of the patterned resist layer, followingexposure at an exposure dose at which the material has a negative tone,has a reflectance of less than 3% for wavelengths in a range from about5 nm to about 20 nm.
 14. The method of claim 8, wherein a material ofthe patterned resist layer has a positive tone at a first exposure doseand a negative tone at a second exposure dose higher than the firstexposure dose.
 15. The method of claim 8, wherein transferring the imagepattern to the hardmask layer and the absorber layer comprises etchingthe hardmask layer and the absorber layer.
 16. A mask for extremeultraviolet (EUV) lithography, the mask comprising: a pattern region;and a border region surrounding the pattern region, the border regionhaving a thickness greater than that of the pattern region andcomprising a resist material.
 17. The mask of claim 16, wherein theresist material has a thickness in a range from about 20 nm to about1000 nm.
 18. The mask of claim 16, wherein the resist material comprisesa polymer and a metal oxide, a metal nitride or metal oxynitride. 19.The mask of claim 16, wherein the resist material comprises metalnitride or metal oxynitride particles having particle size in a rangefrom about 1 nm to about 50 nm.
 20. The mask of claim 16, the resistmaterial comprises a negative photoresist or a negative electron-beamresist.